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More than one in 20 cancer cases attributed to diabetes, BMI

medwireNews: Researchers say that 5.6% of all cancers globally are attributable to the combined effects of diabetes and high BMI.

This 5.6% population attributable fraction (PAF) assumes that diabetes and BMI act at least partly independently on cancer risk; the risk factors individually were responsible for a respective 2.0% and 3.9% of cancers.

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Furthermore, 26.1% and 31.9% of the 792,600 cancer cases reported in 2012 that were attributable to diabetes and BMI, respectively, were caused by the increased prevalence of these risk factors between 1980 and 2002, report Jonathan Pearson-Stuttard (Imperial College London, UK) and study co-authors in The Lancet Diabetes & Endocrinology.

The team assumed a 10-year lag between risk factor exposure and cancer diagnosis, so used 2002 data from the NCD Risk Factor Collaboration and 2012 GLOBOCAN cancer incidence data from the 175 countries for which both were available.

However, writing in an accompanying commentary, Yikyung Park and Graham Colditz, both from Washington University School of Medicine in St Louis, Missouri, USA, argue that this tactic could have caused the researchers to underestimate the impact of BMI and diabetes, citing evidence that high BMI in adolescence and young adulthood may influence cancer risk in old age.

“A focus on adiposity in midlife or later and insufficient consideration of lifetime adiposity could lead to substantial underestimation of the contribution of high BMI to the global burden of cancers, especially given the rapidly increasing prevalence of childhood and adolescent adiposity,” they suggest.

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When the researchers looked at 12 site-specific cancers believed to have a causal link with BMI and/or diabetes, the PAFs were larger still, at 15.0% in men and 13.3% in women. The largest PAFs for these cancers were 28.7% for esophageal cancer in men and 38.4% for endometrial cancer in women. Diabetes and BMI also had relatively large effects (>10% PAF in either gender) on the risk for gallbladder, liver, pancreatic, kidney, and stomach cardia cancer.

The two risk factors independently had varying effects, with, for example, diabetes being responsible for around twice the proportion of pancreatic cancer cases that BMI accounted for, whereas BMI accounted for around three times as many endometrial cancer cases as diabetes did.

There was also regional variability, especially for BMI; its effects ranged from a PAF of 2.7% for cancer cases among men in south Asia to 16.9% for women in central and eastern Europe. This heterogeneity was seen down to the country level within regions, says the team.

Of concern, the researchers expect the prevalence of diabetes- and BMI-attributable cancers to continue increasing. Based on the projected risk factor prevalence for 2025, they believe the PAFs for most site-specific cancers will rise by 20–30%.

“Both obesity and diabetes are preventable causes of cancer for which intervention is possible at multiple levels—in individuals, communities, health-care systems, and policy,” conclude Park and Colditz in their commentary.

“More prompt actions are needed to help people maintain a healthy bodyweight throughout the life course, starting at an early age.”